Project Summary Children show dramatic developments in executive functioning (EF), the goal-directed processes that support flexible adaptation of behavior in response to changing circumstances. For example, children's early- developing forms of EF are reactive, or on-the-fly, based on retrieval of goal-relevant information as needed in the moment. With development, children become increasingly proactive, or planful, maintaining goal-relevant information in anticipation of needing it. Such EFs and their development are associated with benefits to cognition, emotion, and action, and their impairment has been implicated in clinical disorders, including ADHD, autism, OCD, schizophrenia, and Tourette's syndrome. Given this significance for important outcomes, much research has focused on developments in and interventions targeting core EFs such as working memory. However, EFs are diverse rather than unitary or all-purpose, each with relative costs and benefits. Proactive forms of EF bring benefits to preparedness, but also costs in terms of time and effort required prior to actually doing something. Similarly, goal-maintenance can aid staying on task, but confers costs when goal- shifting is required. Such trade-offs require people to coordinate which EFs to engage when, for example, in focusing on one task until it is completed, or switching among several tasks to make progress on each. Thus, children's dramatic improvements in EF may rely upon their self-directed, adaptive coordination of distinct forms of EF, particularly as children gain independence and must determine on their own what tasks to take on, which EFs to engage from their expanding repertoire, and when. Moreover, this adaptive coordination of EFs could explain links between performance on EF measures and significant life outcomes. To address this critical but underexplored aspect of EF, we test developments in the self-directed, adaptive coordination of forms of EF (Aim 1), the factors influencing this coordination (Aim 2), and the trajectories that children show over time (Aim 3), and their relationship to real-world measures. We investigate these processes via cross-sectional and longitudinal studies, using behavioral studies integrated with physiological measures, building on theoretical and empirical work from our lab and others. The studies test: 1) young children, who have demonstrated some capacity for adaptive coordination of EFs, but may rely more on a trial-and-error process sampling from a broad repertoire of potential approaches, 2) older children, who may learn over experience with particular tasks to be increasingly targeted in their adaptive coordination of EFs, and 3) adults, whose adaptive coordination of EFs may be more strategic at the outset across different contexts, reflecting the selection of EFs that are best suited to current demands. We also track children longitudinally as they progress through a key transition window. Together, these studies will advance a new understanding of the role of increasingly adaptive coordination of EFs in development, and provide important constraints and insights for theories and models of executive function and dysfunction more broadly.